Cast Material Research Articles

An implicit solution method for digital construction of temperature fields in concrete structures based on point temperature measurements

PurposeAt present, using the finite element method is difficult to efficiently and accurately construct the temperature field of mass concrete based on temperature measurement points. Thus, there is a need to propose a method for improvement.Design/methodology/approachThis study developed an implicit finite element method that digitally constructs the temperature field of mass concrete based on temperature measurement data. That is, in the proposed method of this paper, the temperature of the measuring point is also one of the boundary conditions, which real-time corrects the calculation error.FindingsIn this method, during the digital construction of the temperature field, the computed temperature approaches the actual measured value at the point of measurement with increasing iteration steps. Using this method and sufficient temperature measurement data, the errors in calculation conditions (such as the boundary conditions, the initial casting temperature and material parameters) can be automatically corrected during the iterative computation process.Originality/valueThis new method can improve calculation accuracy and allows the digitally constructed temperature field to converge to its true value with sufficient measurement data.

Microstructure and Tensile Properties of Ni-Base Superalloy IN738LC according to Solidification Rate and Heat Treatment

The strength of Ni-base superalloys mainly depends on the γ' precipitates that improve the strength of the materials at high temperatures. The presence of γ' particles within the matrix restricts dislocation movement, and optimized heat treatments can tailor the size, shape, and volume fraction of γ'. In this study the effects of solidification rate and solution temperature on the tensile properties of IN738LC superalloy were investigated. The secondary dendritic arm spacing of casting materials with different diameters was measured and the solidification rate of the casting materials was derived by comparing the results of the solidification microstructure obtained from a directional solidification experiment. The D17 material, which had a faster solidification rate, showed higher values of tensile strength and yield strength than the D60 material, which had a slower solidification rate. The study also concluded that the monomodal γ' precipitates in the S80 material have higher tensile strength and yield strength at room temperature and 760℃ than the bimodal γ' precipitates in the S20 material. As for the deformation behavior at 760℃, an isolated stacking fault was observed in the S20 material only within the large γ’ precipitates. In the S80 material, the high dislocation density increased the yield strength due to the strong interaction between dislocations and fine γ’ precipitates.

Effect of Sc addition on downstream processing of twin-roll cast Al−Cu−Li−Mg−Zr-based alloys

A processing scheme for preparing strips of Al−Cu−Li−Mg−Zr-based alloys microalloyed with Sc was proposed. This scheme includes a twin-roll casting of strips with a near-net-shaped 3 mm-thick gauge and a homogenization/solution treatment processing step. Two twin-roll cast Al−Cu−Li−Mg−Zr-based alloys were studied, one with an addition of 0.17 wt.% Sc, and the other without addition of Sc. Both alloys were annealed at 300 °C for 30 min, 450 °C for 30 min, and 530 °C for 30 min and quenched into room temperature water. The first two annealing steps provide a fine dispersion of Al3Zr/Al3(Sc,Zr) particles. The final annealing step serves as homogenization/solution treatment. A fine crystallization structure of the twin-roll cast materials enables the dissolution of primary particles containing the main alloying elements during a relatively short annealing time. Shorter soaking duration limits the depletion of surface layers from Li and significant coarsening of Al3Zr/Al3(Sc,Zr) dispersoids. The Sc-containing material has significantly finer grains already in the as-cast state. The Al3(Sc,Zr) dispersoids formed during the homogenization/solution treatment step prevent grain coarsening at high temperatures. Strengthening θ′(Al2Cu), T1(Al2CuLi), and rare S’(Al2CuMg) phases are formed during subsequent artificial aging at 180 °C. The increase in yield strength was 200 MPa in the peak-aged conditions. This value is comparable to the ones reported in similar direct-chill cast materials, thus validating the proposed processing scheme.

Advancements in Dental Casting Materials & Their Forensic Significance

Abstract: This research explores various dental casting materials & their significance in forensic science. Traditional materials, such as- Dental stone, Plaster of Paris, & Dental wax have long been utilized in forensic investigations. However, advancements in materials science have led to the development of newer, more versatile options, such as- Epoxy resins, Polyurethane, & Alginate substitutes. Each material offers distinct advantages & limitations concerning ease of use, accuracy, & durability. Dental stone, a widely used & employed material, provides excellent detail reproduction & stability but lacks flexibility. Plaster of Paris, though economical, may not yield precise replicas due to its brittle nature. Dental wax, appreciated for its malleability & is susceptible to form deformation & degradation over time. In contrast, modern alternatives like- Epoxy resins & Polyurethane boast superior strength & dimensional stability, making them ideal for long-term storage of dental impressions. Epoxy resins, in particular, offer high fidelity reproduction of dental structures & resistance to moisture, temperature fluctuations. Polyurethane, known for its flexibility & durability, enables the creation of resilient dental models suitable for extensive forensic analysis. Furthermore, Alginate substitutes have gained popularity for their ease of use & compatibility with 3D Printing technology. These materials also offer quick setting times & adequate detail capture, facilitating rapid production of dental models for forensic examination. While, Traditional materials continue to serve a purpose, the adoption of advanced casting materials has revolutionized forensic odontology by enhancing- efficiency, precision & archival integrity

Fabrication of Y2O3–CaO composite ceramics with controllable hydration resistance by a novel gel casting method

Y2O3 and CaO are ideal ceramic materials for precision casting of TiAl alloy, overcoming challenges associated with intricate component removal, such as turbine blades, leveraging the stability of Y2O3 and the water solubility of CaO. To address these challenges, we employed Isobam104 in a novel gel casting method, serving as both a dispersant and a gelling agent. This method enabled us to create a stable Y2O3–CaCO3 slurry with high solid content (up to 55 vol%) and low viscosity (101.51 mPa·s at a shear rate of 10 s−1). Following sintering at 1500 °C for 2 h, Y2O3–CaO composite ceramics were produced. Surprisingly, two distinct characteristics of CaO were noted. One showed a rod-shaped morphology with high chemical reactivity crucial for water solubility, while the other displayed a flat-like feature, forming a well-maintained interface due to its coherent or semi-coherent matching relationship with Y2O3, thereby providing excellent hydration resistance. Ultimately, we acquired composite ceramics showcasing a 30-day “shelf life" alongside exceptional water solubility. This establishes the theoretical groundwork for storing and employing soluble ceramic cores in the precision casting of TiAl alloy.

Study on the dynamic response characteristics of lining structures in large-section tunnel blasting using JH-2 model analysis

The lining structures of tunnels are typically constructed using sprayed or cast concrete materials, and their performance and quality during tunnel excavation and blasting are crucial for the stability and safety of tunnels. Therefore, the safe distance between the lining structure and blasting source should be determined to avoid concrete damage caused by blasting vibrations. In this study, taking the subway tunnel of Danshan Station in Qingdao as an example, the JH-2 model is introduced as the constitutive model of the tunnel blasting simulation, and the JH-2 model parameters of the local surrounding rock are obtained by experiments, and finally the numerical simulation and theoretical verification are carried out to study the safety distance of shotcrete under various safety judgment standards. The results indicate that the JH-2 model can effectively simulate the propagation of stress waves under different media conditions, and the closer the strength parameters and pressure constant of the lining structure are to those of the surrounding rock, the safer the concrete–rock bonding interface. During tunnel blasting construction using the ring blasting method, the peak particle velocity (PPV) of the lining structure increases with an increase in the arch angle. Based on the numerical simulation results, we recommend that concrete lining be constructed at a distance of at least 62 m from the blasting source to avoid damage caused by vibrations. The effect of concrete tensile failure caused by longitudinal stress is much smaller than the damage to the bonding interface caused by the PPV and can be neglected.

Preparation of a graphite / SiC composite casting material and study of its performance

The inferior mechanical properties and thermal conductivity of carbon graphite materials are attributed to the presence of pores and cracks. The integration of graphite with ceramics has been proposed as a method to enhance these properties; however, graphite/ceramic composites fabricated through pressureless sintering often exhibit inadequate integration. In this paper, a diffuse-continuous network dual-reinforced graphite/silicon carbide(SiC) ceramic composite was prepared by integrating the graphite powder micro-thermal press forming technology with the fused deposition modelling(FDM) technology and combining the pressureless sintering and vacuum pressure impregnation processes. It was found that the addition of high purity silicon powder to the material formulation reacts with the resin carbon to form silicon carbide particles (SiC-p), which can play a role in diffusion enhancement. However, the addition of excessive silicon powder can have a detrimental effect, and the performance of diffusion enhanced graphite/silicon carbide composites is positively correlated with the density of billet formation, and the effect of diffusion continuous network dual enhancement is more obvious, and the performance of the composites is better compared to that of single diffusion enhancement. The compressive and flexural strengths of the graphite/SiC composites finally obtained reached 59.47 MPa and 44.25 MPa, respectively, and the thermal conductivity was 43.62 W/m·K, and the porosity and open porosity were 29.62 % and 20.48 %, respectively, which are comparable to those of manmade graphite castings, and have better gas permeability, which is expected to be applied in the casting field.

Feasibility study on hybrid manufacturing – combining laser‐based powder‐bed fusion and chill casting on the example of EN AC‐42000 alloy

AbstractLaser‐based powder‐bed fusion can be combined with casting into a hybrid manufacturing process. This is done to simultaneously utilize advantages of both processes. To examine related challenges stemming from this combination when using aluminium alloys, first experiments were conducted with EN AC‐42000 alloy, an alloy common in both standalone processes. EN AC‐42000 alloy samples with different surface treatments were placed into a sand mould and cast on to with an aluminium melt. The contact region between the partially molten insert and the cast material was examined with light microscopy. The main challenges were shown to be comprised of bonding issues due to present oxides and a high porosity. The high porosity was traced back to a porosity increase in the laser‐based powder‐bed fusion insert.

Exploring sustainable aesthetics through repurposed studio waste materials for unorthodox finishes

This study recycles and repurposes discarded studio waste materials, such as broken ceramics, glass fragments, sawdust, and bits of shattered P.O.P molds, to create visually compelling creative works. The interest for this study is inspired by the prolific generation of waste that arises from the studio learning practices of sculpture and ceramic students. A studio-based research approach utilizing Aesthetico-Action Research design is employed in a systematic approach to explore the feasibility and promise of composite amalgamation. The researchers mix resin and fiberglass composite materials with the various types of studio waste. The primary objective is to achieve creative outcomes with unconventional and unique finishes. The technique, philosophical and symbolic application, and usage of these materials in creating distinct art pieces including an exclusive “African woman” offer intriguing insights. The study reveals that the studio can efficiently repurpose waste materials, creating new cast materials for sculptures and ceramic works with distinctive and non-traditional finishes. This highlights the intrinsic transforming capacity of disposable waste materials, presenting a compelling opportunity for new and sustainable artistic practice where material finishes are not concealed.

Evaluating the joinability of thin-walled high pressure die cast aluminium for automotive structures using self-piercing rivets

This paper is the first to report successful application of self-pierce riveting (SPR) in thin-walled high pressure die cast (HPDC) aluminium for use in automotive applications. HPDC fabricated AA356x coupons were joined to conventional rolled RC5754 material. A set of industry-relevant joint stacks were created. Priority stacks included cast material as the upper layer. More challenging joints were also fabricated with cast material as the lower layer. Automotive industry key performance indicators were used to assess joint integrity. The key results and recommendations were:•HPDC aluminium was revealed to be able to be joined to rolled aluminium according to vehicle manufacturer automotive standards.•Process boundaries were established for satisfactory SPR joints across a range of material thicknesses and stack types.•SPR joint solutions were proven in the most challenging stacks with cast material as a bottom layer.•Greater variability in the joint key performance indicators was observed in stacks where the cast alloy is the top layer.•Microstructural analysis of both AA356x and RC5754 revealed differences in grain structure and hardness and it is proposed that this accounts for the increased variability.•Strength testing of lap shear joints demonstrated the mechanical effectiveness of an SPR joint including cast material. Under normal vehicle operating conditions, the performance of joints including cast material was equivalent to that of rolled material only joints. Following yielding, joints including cast material suffered a more brittle failure mode leading to differences in performance under crash scenarios.

Mechanical Properties of a Structural Component Processed in High-Pressure Die Casting (HPDC) with a Non-Heat-Treated Aluminum Alloy

This industrial research focuses on the implementation and development of a productive process for an automotive structural component (Shock tower) manufactured by a high-pressure die casting (HPDC) process made of aluminum alloy AuralTM-5. This aluminum alloy has been considered in diverse automotive and aerospace components that do not require heat treatment due to its mechanical properties as cast material (F temper). On the other hand, AuralTM-5 has been designed for processing as HPDC because it is an alloy with good fluidity, making it ideal for large castings with thin-wall thicknesses, like safety structural components such as rails, supports, rocker panels, suspension crossmembers, and shock towers. The mechanical properties that were evaluated for the evaluated components were yield strength, ultimate tensile strength, and elongation. Eight samples were taken from different areas of each produced shock tower for evaluating and verifying the homogeneity of each casting. The samples were evaluated from the first hours after they were manufactured by casting until eight weeks after being produced. This was performed to understand the behavior of the alloy during its natural aging process. Two groups of samples were obtained. One set of components was heat-treated by a water quench process after the castings’ extraction and the other set of components was not quenched. Results demonstrated that both sets of components, quenched and not quenched, achieved the expected values for the AuralTM-5 of yield strength ≥ 110 MPa, ultimate tensile strength ≥ 240 MPa, and elongation ≥ 8%. Additionally, this is very important for industry since by not treating the structural components by quenching, there are savings in terms of infrastructure and energy consumption, together with benefits in the environmental aspect by avoiding CO2 emissions and being sustainable.

ANALYSIS OF WASTE MATERIAL COEFFICIENT FOR CONCRETE CASTING WORK USING BIM CUBICOST TAS

One of the construction project activities that has a large volume of work on the upper structure is casting work. In concrete requirement planning, contractors usually multiply the book by 10%. However, in practice, the concrete requirement is still less than planned. Therefore, concrete requirement planning must be calculated accurately. The volume of concrete needs to be multiplied by the waste material coefficient. This research was conducted on the XYZ Project by directly observing to obtain the volume of realized concrete purchased so that the value of the material coefficient that has taken into account waste material will be obtained. BIM Cubicost TAS is used to minimize planning volume calculation errors. The results of this study show that for horizontal casting work, the largest percentage of residual material is 3.133%, and the average percentage of residual material for horizontal casting is 2.192%. Meanwhile, for vertical casting work, the largest percentage of remaining material is 7.219% and the average percentage of remaining vertical casting material is 3.015%. Finally, the waste material coefficient is obtained as 1.022 for horizontal casting and 1.03 for vertical casting. In the AHSP Ministerial Regulation No. 1 of 2022, the coefficient value of materials for casting work using ready-mix concrete is 1.02. This reveals that the coefficient value in AHSP Minister of Public Works and Public Housing Regulation No. 1 of 2022 has not fully calculated the real waste material in the field. The analyzed coefficient values in this study can be used as a reference for the project to determine coefficients in the AHSP and aid in planning concrete volume requirements because it already takes into account the real waste material in the field.

Pore evolution in extrusion-based 3D printed cementitious materials due to calcium leaching

Extrusion-based 3D printed cementitious materials (3DPC) require specific parameters to be met that will substantially impact printed part durability, particularly when exposed to aggressive external conditions. Due to the specificity of the spatial distribution of the pores, 3DPC are reported to exhibit performance anisotropy compared to cast materials. A fundamental understanding of the discrepancy in the pore evolution between the printing direction, lateral direction, and top direction is essential for calcium leaching from 3DPC in aggressive water. This research investigates pore structure evolution in 3DPC with the three directions in a 6 mol/L ammonium chloride solution. The leaching depths of the samples in the three directions were tested and compared. In addition, their porosity, maximum, median, and average pore diameters, pore size distribution, and pore morphology are investigated using optical microscope (OM) and mercury intrusion porosimetry (MIP) analysis. Significant differences were found between the leaching depths in the different directions of the 3DPC. Samples leached in the top direction show less leaching depth than in the other two directions, indicating the anisotropic nature of 3DPC. This was attributed to the different pore structures of the sample in the top direction compared to the other directions, as confirmed by OM and MIP analysis. Furthermore, the pore morphology is more irregular and elongated in the printing and lateral directions than in the top direction. In turn, the calcium leaching increases the porosity and coarsens the pore structure of 3DPC. The results of this study can be used as a reference for the application of 3DPC in aggressive water environments.

Investigations on the Degradation Behavior of Processed FeMnSi-xCu Shape Memory Alloys.

A new functional Fe-30Mn-5Si-xCu (x = 1.5 and 2 wt%) biomaterial was obtained from the levitation induction melting process and evaluated as a biodegradable material. The degradation characteristics were assessed in vitro using immersion tests in simulated body fluid (SBF) at 37 ± 1 °C, evaluating mass loss, pH variation that occurred in the solution, open circuit potential (OCP), linear and cyclic potentiometry (LP and CP), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and nano-FTIR. To obtain plates as samples, the cast materials were thermo-mechanically processed by hot rolling. Dynamic mechanical analysis (DMA) was employed to evaluate the thermal properties of the smart material. Atomic force microscopy (AFM) was used to show the nanometric and microstructural changes during the hot rolling process and DMA solicitations. The type of corrosion identified was generalized corrosion, and over the first 3-5 days, an increase in mass was observed, caused by the compounds formed at the metal-solution interface. The formed compounds were identified mainly as oxides that passed into the immersion liquid. The degradation rate (DR) was obtained as a function of mass loss, sample surface area and immersion duration. The dynamic mechanical behavior and dimensions of the sample were evaluated after 14 days of immersion. The nanocompounds found on the surface after atmospheric corrosion and immersion in SBF were investigated with the Neaspec system using the nano-FTIR technique.

Assessment of mechanical and tribological behavior of Mg-4Zn-1RE-0.7Zr alloy: Novel mixture of Si3N4/TiC/MoS2 utilizing casting technique

In the modern era, manufacturers aim for their parts to possess a sleek finish and increased durability to ensure continued functionality. Both the automotive and aerospace industries are actively seeking new materials and methodologies to enhance the surface quality of components during the preparation process and make the most of available resources. Employing casting, advanced techniques, and new materials is crucial for achieving this goal. Industries commonly utilize alloys and composite materials in the production of their components. This study focuses on magnesium composite Mg-4Zn-1RE-0.7Zr alloy to find the influence of varying three different reinforcement particles on mechanical properties and wear rate. An attempt was made to choose a constant 5% Si3N4 as the primary reinforcement and 2.5% to 7.5% of TiC/MoS2 as the secondary reinforcement, respectively. The samples of magnesium hybrid composites are prepared using a centrifugal casting process. The ZE 41 alloy/5% (TiC-MoS2)/5%Si3N4 has a high tensile strength of 942 MPa. In addition, 5% TiC/5% MoS2 with 5% Si3N4 composite has enhanced hardness, which is beneficial for transmission in aircraft like Boeing 727 and die-casting fittings in automobile applications.

Near Net Shape Manufacturing of Sheets from Al-Cu-Li-Mg-Sc-Zr Alloy.

Thin twin-roll cast strips from a model Al-Cu-Mg-Li-Zr alloy with a small addition of Sc were prepared. A combination of a fast solidification rate and a favorable effect of Sc microalloying refines the grain size and the size of primary phase particles and reduces eutectic cell dimensions to 10-15 μm. Long-term homogenization annealings used in conventionally cast materials lasting several tens of hours followed by a necessary dimension reduction through rolling/extruding could be substituted by energy and material-saving procedure. It consists of two-step short annealings at 300 °C/30 min and 450 °C/30 min, followed by the refinement and hardening of the structure using constrained groove pressing. A dense dispersion of 10-20 nm spherical Al3(Sc,Zr) precipitates intensively forms during this treatment and effectively stabilizes the structure and inhibits the grain growth during subsequent solution treatment at 530 °C/30 min. Small (3%) pre-straining after quenching assures more uniform precipitation of strengthening Al2Cu (θ'), Al2CuMg (S'), and Al2CuLi (T1) particles during subsequent age-hardening annealing at 180 °C/14 h. The material does not contain a directional and anisotropic structure unavoidable in rolled or extruded sheets. The proposed procedure thus represents a model near net shape processing strategy for manufacturing lightweight high-strength sheets for cryogenic applications in aeronautics.

On the properties of cast and powder metallurgical Cu–6Ni-1.5Si-0.15Al (wt.%) alloy

In this study, Cu–6Ni-1.5Si-xAl (x = 0 and 0.15 wt%) alloys are manufactured as billet materials by casting and their metallurgical and physical properties are characterized. Aluminum modified alloy is obtained also by a powder metallurgical (PM) route and its structural properties are determined to be compared with the cast materials. The findings indicate that (i) solidified alloys have distributed nickel silicides (27.01 %) embedded in α-Cu(Ni,Si) solid solution, (ii) the addition of aluminum increases the amount of silicides (29.09 %) in the solidified matrix and reduces both the grain size and the secondary dendrite arm spacing, (iii) although PM alloy has similar microstructural features as cast alloys, it exhibits the highest hardness (159 HV1) due to both finer grain structure and better distribution of silicides, (iv) both impurity and porosity have a determining effect on the electrical conductivity (27–32 % IACS, International Annealed Copper Standard) values of the alloys.

Tribological Performance of Copper-Based Composites as Tribopairs of Piston Pumps

To develop superior piston pump friction pair materials in harsh working conditions, the tribological properties of two novel copper-based composites, C93800 copper alloy casting material and 10–10 powder metallurgy copper steel bimetallic plate, as tribo-pairs of a piston pump were evaluated on an end-face tribometer. Their tribological behavior and extreme pressure x velocity (PV) values (PV value is an important indicator that reflects the performance of sliding bearings and is the product of the unit bearing load and the restricted linear speed) were analyzed. The results show that both the two copper-based composites had excellent antifriction and antiwear performances. The 10–10 powder metallurgy copper steel bimetallic plate shows better wear resistance and superior tribological performance due to its higher hardness. However, its extreme PV value is lower than the C93800 copper alloy casting material, since the latter can play a buffer during the loading process. In addition, the extreme PV value of the C93800 copper alloy casting material amounted to 40 MPa·m/s, showing promising potential for industrial application.

The Microstructure and Magnetic Properties of a Soft Magnetic Fe-12Al Alloy Additively Manufactured via Laser Powder Bed Fusion (L-PBF)

Soft magnetic Fe-Al alloys have been a subject of research in the past. However, they never saw the same reception in technical applications as the Fe-Si or Fe-Ni alloys, which is, to some extent, due to a low ductility level and difficulties in manufacturing. Additive manufacturing (AM) technology could be a way to avoid issues in conventional manufacturing and produce soft magnetic components from these alloys, as has already been shown with similarly brittle Fe-Si alloys. While AM has already been applied to certain Fe-Al alloys, no magnetic properties of AM Fe-Al alloys have been reported in the literature so far. Therefore, in this work, a Fe-12Al alloy was additively manufactured through laser powder bed fusion (L-PBF) and characterized regarding its microstructure and magnetic properties. A comparison was made with the materials produced by casting and rolling, prepared from melts with an identical chemical composition. In order to improve the magnetic properties, a heat treatment at a higher temperature (1300 °C) than typically applied for conventionally manufactured materials (850–1150 °C) is proposed for the AM material. The specially heat-treated AM material reached values (HC: 11.3 A/m; µmax: 13.1 × 103) that were close to the heat-treated cast material (HC: 12.4 A/m; µmax: 20.3 × 103). While the DC magnetic values of hot- and cold-rolled materials (HC: 3.2 to 4.1 A/m; µmax: 36.6 to 40.4 × 103) were not met, the AM material actually showed fewer losses than the rolled material under AC conditions. One explanation for this effect can be domain refinement effects. This study shows that it is possible to additively manufacture Fe-Al alloys with good soft magnetic behavior. With optimized manufacturing and post-processing, further improvements of the magnetic properties of AM L-PBF Fe-12Al may still be possible.

The Impact of HIP Process and Heat Treatment on the Mechanical Behaviour of an Al–Si–Mg Alloy Component

AbstractThis study investigates the effect of hot isostatic pressing (HIPping) on the static and fatigue properties of sand-casting A356 aluminium alloys. HIPping is a method to improve the fatigue properties in aluminium cast material by reducing or eliminating the inner porosities. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIPping process was examined using computed tomography and scanning electron microscopy (SEM). Castings generally contain pores and defects that have a detrimental impact on the fatigue properties. The HIPping process closes the porosities in all investigated samples with an increase in density. Without significant defects, the mechanical performance improved in the finer microstructure. However, a considerable variation in the results was found between the different conditions, whereas the coarser microstructure with larger porosities before HIPping showed remarkably reduced results. The high-cycle fatigue-tested samples showed reduced fatigue propagation zone in the coarser microstructure. Moreover, large cleavage areas containing bifilms in the fracture surfaces indicate that the healing process of porosities is inefficient. These porosities are closed but not healed, resulting in a detrimental effect on the static and dynamic properties.